Method and system for electro-assisted hydrogen production from organic material

Abstract

A method for producing hydrogen from organic material. Organic material and hydrogen-producing microorganisms are provided in a completely mixed bioreactor for breaking down the organic material into H.sub.2, CO.sub.2, fatty acids, and alcohols. H.sub.2, CO.sub.2, and a first liquid effluent are recovered from the completely mixed bioreactor. The first liquid effluent includes hydrogen-producing microorganisms, fatty acids, and alcohols. The first liquid effluent is provided into a gravity settler for separating the first liquid effluent into a concentrated biomass (including hydrogen-producing microorganisms) and a second liquid effluent (including at least a portion of the fatty acids and the alcohols). The concentrated biomass is provided into the completely mixed bioreactor. An input voltage is applied to at least one of the completely mixed bioreactor and the gravity settler for facilitating an electrohydrogenesis process therein.

Claims

1. A method for producing hydrogen from bio-organic material by microbial electrolysis, comprising: generating a dark fermentation broth by providing bio-organic material and anaerobic, hydrogen-producing microorganisms into a completely mixed bioreactor for breaking down the bio-organic material by dark fermentation into products including H.sub.2, CO.sub.2, fatty acids, and alcohols; recovering at least a portion of the H.sub.2 and of the CO.sub.2 from the completely mixed bioreactor; recovering a first liquid effluent from the completely mixed bioreactor, the first liquid effluent including at least a portion of the hydrogen-producing microorganisms, the fatty acids, and of the alcohols; providing at least a portion of the first liquid effluent into a separator for separating into a concentrated biomass including at least a portion of the hydrogen-producing microorganisms and a second liquid effluent including at least a portion of the fatty acids and the alcohols; recycling at least a portion of the concentrated biomass from the separator back into the completely mixed bioreactor; and applying an input voltage to at least one of the completely mixed bioreactor and the separator for facilitating an electrobiohydrogenesis process in the at least one of the completely mixed bioreactor and the separator.

2. The method of claim 1, wherein the separator is a gravity settler.

3. The method of claim 2, wherein applying the input voltage comprises applying the input voltage to the completely mixed bioreactor.

4. The method of claim 2, further comprising recovering at least a portion of the H.sub.2 and of the CO.sub.2 from the gravity settler.

5. The method of claim 4, wherein applying the input voltage comprises applying the input voltage to the gravity settler, and the method further comprises recovering at least a portion of H.sub.2 and CO.sub.2 produced by electrobiohydrogenesis in the gravity settler.

6. The method of claim 5, wherein the temperature in the gravity settler is maintained at between about 20 C. and about 70 C.

7. The method of claim 1, wherein the temperature in the completely mixed bioreactor is maintained at between about 20 C. and about 70 C.

8. The method of claim 1, wherein the input voltage is between about 0.5 V and about 1.8 V.

9. The method of claim 8, wherein the input voltage is about 1.0 V.

10. The method of claim 1, wherein the input voltage is a continuous voltage.

11. The method of claim 1, wherein the input voltage is an intermittent voltage.

12. The method of claim 1, further comprising providing the second liquid effluent into a biomethanator for production of methane from the second liquid effluent.

13. The method of claim 12, further comprising providing the second liquid effluent into a storage tank prior to providing the second liquid effluent into the biomethanator.

14. The method of claim 12, wherein the temperature in the biomethanator is maintained at between about 20 C. and about 70 C.

15. The method of claim 1, wherein the anaerobic, hydrogen producing microorganisms comprise one or more of the species selected from the group consisting of C. acetobutyricum, B. thuringiensis, and C. butyricum.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a schematic illustration of an electrobiohydrogenator reactor and gravity settler;

(2) FIG. 2 is a schematic illustration of an biohydrogenator reactor and electro-assisted gravity settler;

(3) FIG. 3 is a schematic illustration of an electrobiohydrogenator reactor, gravity settler, storage tank, and biomethanator reactor;

(4) FIG. 4 is an embodiment of an electrode assembly and electrobiohydrogenator reactor of FIG. 1 or 3;

(5) FIG. 5 is a plot of acetate consumption and hydrogen production during a tenth cycle of voltage being applied to an electrobiohydrogenator reactor;

(6) FIG. 6 is a plot of acetate consumption and hydrogen production during an eleventh cycle of voltage being applied to the electrobiohydrogenator reactor of FIG. 5; and

(7) FIG. 7 is a plot of acetate consumption and hydrogen production during a twelfth cycle of voltage being applied to the electrobiohydrogenator reactor of FIG. 5.

DETAILED DESCRIPTION

(8) The process and system herein provided involve application of two processes for hydrogen production and treatment of waste: dark fermentation and electro-assisted fermentation. The process and system herein provided are directed to mitigating some drawbacks of previous techniques for sustained biological hydrogen production: contamination of microbial hydrogen-producing cultures with methane-producing cultures (sometimes necessitating frequent re-start-up or other methanogenic bacteria inactivation techniques), low bacterial yield of hydrogen-producers culminating in microbial washout from the system and failure, and a maximum hydrogen yield of 3.2 mol H.sub.2/mol glucose reported for dark fermentation out of the theoretical maximum of 12 mol H.sub.2/mol glucose.

(9) In Liu et al. (2005), it was postulated that based on dark fermentation and electrohydrogenesis processes, the overall hydrogen yield can be as high as 8-9 mol H.sub.2/mol hexose, although they verified experimentally and in batch studies only that 1 mole of acetate can produce as much as 2.9 moles of hydrogen using electrohydrogenesis. Thus it has not been proven experimentally using continuous flow systems that a single bioreactor process of simultaneous dark fermentation and electrohydrogenesis could be successfully operated, nor whether 8-9 mol H.sub.2/mol glucose can be sustained in such a single bioreactor process.

(10) Interpretation

(11) As used herein, the term about, when used in conjunction with ranges of dimensions, concentrations, temperatures or other physical or chemical properties or characteristics is meant to cover slight variations that may exist in the upper and lower limits of the ranges of properties or characteristics.

(12) As used herein, the phrases completely mixed bioreactor or continuously stirred tank reactor (CSTR) mean a mechanically or hydraulically agitated vessel including microorganisms in suspension and a growth media, typically including nutrients such as organic carbon, nitrogen-containing compounds, phosphorous-containing compounds, and trace mineral solutions.

(13) As used herein, the phrase hydrogen producing microorganisms means microorganisms capable of fermenting organics under anaerobic conditions to produce hydrogen, carbon dioxide, and a variety of organic acids and alcohols.

(14) As used herein, the phrase organic waste refers to wastes that include carbon and hydrogen such as, but are not limited to, alcohols, ketones aldehydes, VFAs, esters, carboxylic acids, ethers, carbohydrates, proteins, lipids, polysaccharides, monosaccharide, cellulose, and nucleic acids. Organic waste may originate, for example, from high strength industrial waste waters, such as those commonly associated with the food and agriculture sector, bioethanol industries, and young landfill leachates from non-hazardous waste disposal sites.

(15) As used herein, the terms comprises, comprising, includes and including are to be construed as being inclusive and open ended, and not exclusive. Specifically, when used in this specification including claims, the terms comprises, comprising, includes and including and variations thereof mean the specified features, steps or components are included. These terms are not to be interpreted to exclude the presence of other features, steps or components.

(16) Electrobiohydrogenator System and Electrobiohydrogenation Process

(17) Referring to FIG. 1, an electrobiohydrogenator system 10 for producing hydrogen and methane from organic waste in an electrobiohydrogenation process is shown. The system 10 includes a completely mixed bioreactor 14 (e.g. a CSTR) having an input for receiving organic material 12 (e.g. organic waste) into the completely mixed bioreactor 14. A gravity settler 16 (also referred to as a clarifier) is located downstream of the completely mixed bioreactor 14 and hydraulically connected with an outlet of the completely mixed bioreactor 14 for receiving a first effluent 18 from the completely mixed bioreactor 14. The system 10 includes hydrogen producing microorganisms located in the completely mixed bioreactor 14 for breaking down the organic material 12.

(18) A lower portion of the gravity settler 16 is hydraulically connected to the completely mixed bioreactor 14 for recirculating settled biomass 24 from the gravity settler 16 to the completely mixed bioreactor 14 (for example through a feedback conduit). For example, the settled biomass 24 may be mixed with the organic material 12 being provided to the completely mixed bioreactor 14. Recirculation of settled biomass 24 from the gravity settler 16 to the completely mixed bioreactor 14 maintains the biomass concentration at the desired range.

(19) When dark fermentation is carried out, glucose may be converted to H.sub.2, CO.sub.2, and either acetate or butyrate by the reactions shown below in equations (1) and (2), respectively:
C.sub.6H.sub.12O.sub.6.fwdarw.2CH.sub.3COOH+2CO.sub.2+4H.sub.2G=206 KJ(1)
C.sub.6H.sub.12O.sub.6+2H.sub.2O.fwdarw.CH.sub.3CH.sub.2CH.sub.2COOH+2CO.sub.2+2H.sub.2G=254 KJ(2)

(20) The acetate and butyrate may then in turn each be converted into further H.sub.2 and CO.sub.2 by the reactions shown below in equations (3) and (4):
CH.sub.3COOH+2H.sub.2O.fwdarw.2CO.sub.2+4H.sub.2G=+94.9 KJ(3)
CH.sub.3CH.sub.2CH.sub.2COOH+6H.sub.2O.fwdarw.4CO.sub.2+10H.sub.2G=+48.3 KJ(4)

(21) An external voltage may be applied for overcoming the positive G values associated with the reactions of equations 3 and 4 (and making the G values associated with the reactions of equations 1 and 2 more negative). For example, a voltage of between about 0.5 V and about 1.8 V may be applied depending on many factors (e.g. desired products formation, external and internal resistance of the system, etc.).

(22) In addition to the completely mixed bioreactor 14 for biological hydrogen production and the gravity settler 16, the system 10 includes an electrode arrangement 30 for the application of an input voltage. The electrode arrangement 30 includes an anode 31 and cathode 32. The electrode arrangement 30 may be placed at one or more of two alternative locations in the system 10. In FIG. 1, the electrode arrangement 30 is placed in the continuously mixed bioreactor 14 (providing an electrobiohydrogenator reactor). In FIG. 2, the electrode arrangement 30 is placed in the gravity settler 16 (providing an electro-assisted gravity settler). The gravity settler 16 of FIG. 2, which includes the electrode arrangement 30, is a covered gravity settler for facilitating recovery of the H.sub.2 and CO.sub.2 produced in the gravity settler 16. VFAs are present in both the completely mixed bioreactor 14 and the gravity settler 16, and are the main soluble metabolites in the gravity settler 16. Integration of the electro-assisted process into the system 10 is accomplished by submerging the electrode arrangement 30 in the continuously mixed bioreactor 14 (FIG. 1), the gravity settler 16 (FIG. 2), or both (not shown), and supplying an input voltage. The input voltage may be continuous, intermittent, or both. The electrode material can be, for example, platinum, graphite, or stainless steel. The voltage at pH 7 required to produce hydrogen is theoretically 0.61 V (Vcat versus Ag/AgCl). The anode potential produced by the bacterial oxidation of the organic matter is about 0.50 V (Van), so the minimum theoretical applied voltage is 0.11 V (Vapp=VanVcat). In practice, the minimum applied voltage to produce hydrogen from the bioelectrolysis of acetate has been found to be more than 0.25 V due to ohmic resistance and electrode overpotential, which is still substantially less than the 1.8-2.0 V needed for hydrogen production via water electrolysis (alkaline conditions).

(23) The method and system may be practiced with varying schedules of operation with respect to applying power to the electrode arrangement 30. For example, the frequency of power application cycles may be adjusted to apply the method and operate the system on a 24 hour schedule.

(24) Hydrogen gas (H.sub.2), carbon dioxide (CO.sub.2), and the first effluent 18, are emitted from the completely mixed bioreactor 14. The first liquid effluent 18 includes VFAs, primary alcohols and hydrogen-producing microorganisms. The H.sub.2 and CO.sub.2 are recovered. The first liquid effluent 18 flows to the gravity settler 16. The hydrogen producing microorganisms settle to the bottom of, and are concentrated in, the gravity settler 16. The settled hydrogen-producing microorganisms in the bottom of the gravity settler 16 are recirculated back to the completely mixed bioreactor 14, leaving a second liquid effluent 28 in the gravity settler 16.

(25) FIG. 3 shows an embodiment of the system 10 including a biomethanator 22. The second liquid effluent 28 from the gravity settler 16 is loaded with residual VFAs that were not converted to hydrogen during power application in either or both configurations of the electrode arrangement 30 (e.g. electrobiohydrogenator reactor and gravity settler, biohydrogenator reactor and electro-assisted gravity settler, or electrobiohydrogenator reactor and electro-assisted gravity settler) as a result of microbiological breakdown of the influent waste constituents by hydrogen-producing bacteria, and is an excellent substrate for methane-forming bacteria. Thus, the second effluent 28 can advantageously be directed to the biomethanator 22. Production of VFAs in the completely mixed bioreactor 14 may improve the efficiency of the second-stage biomethanator 22, for example by increasing the volumetric methane production rate, methane yield, or solids destruction efficiency, thus allowing for higher volumetric and organic loading rates. It is expected that the aforementioned beneficial impact of the system 10 on this second-stage anaerobic treatment process is independent of the second-stage biomethanator 22 reactor design and/or configuration.

(26) As also shown in FIG. 3, the system 10 may include a storage tank 26 hydraulically connected to and located downstream of, the gravity settler 16. The storage tank 26 may be located upstream of the optional biomethanator 22, and hydraulically connected to both the gravity settler 16 and biomethanator 22 for adjusting loading rates of the liquids entering the biomethanator 22.

(27) The system 10 may include a dispenser (not shown) for dispensing chemicals into the storage tank 26 for adjusting alkalinity, pH, or other properties of the liquid in the storage tank 26. The system 10 may also include a dispenser (not shown) for dispensing nutrients and pH adjustment compounds into the completely mixed bioreactor 14. The nutrients may include any one or combination of: nitrogen containing compounds, phosphorous containing compounds and trace metals (including iron, manganese, magnesium, calcium, cobalt, zinc, nickel, and copper). The pH adjustment compounds may include soda ash, sodium bicarbonate, sodium hydroxide, calcium hydroxide, magnesium hydroxide, nitric acid, and hydrochloric acid.

(28) Examples of hydrogen generating microorganisms include C. acetobutyricum, B. thuringiensis, and C. butyricum.

(29) The system 10 may also include temperature controllers for controlling the temperature in the completely mixed bioreactor 14, in the biomethanator 22 or both. A typical temperature range in which the temperature of the contents of both the completely mixed bioreactor 14 and the biomethanator 22 is maintained may be from about 20 C. to about 70 C. Where the gravity settler 16 is an electro-assisted gravity settler (e.g. FIG. 2), the gravity settler 16 may include temperature controllers for controlling the temperature in the range of 20 C. to about 70 C.

Example I

(30) A lab-scale conventional biohydrogenator was operated at 37 C. with an organic loading rate of 25.7 gCOD/L-d (gCOD is a measure of COD in grams). The biohydrogenator included a CSTR for biological hydrogen production (5 L working volume) hydraulically connected to an uncovered (i.e. open to atmosphere) gravity settler (volume 8 L) for the decoupling of SRT from HRT. The feed contained the following inorganics: 2000-16000 mg/L NaHCO.sub.3; 140 mg/L CaCl.sub.2; 160 mg/L MgCl.sub.2.6H.sub.2O; 600 mg/L NH.sub.4HCO.sub.3; 160 mg/L MgSO.sub.4.7H.sub.2O; 500-2000 mg/L urea, 124-300 mg/L Na.sub.2CO.sub.3; 156 mg/L KHCO.sub.3; 15-20 mg/L K.sub.2HPO.sub.4; 500 mg/L trace mineral solution; and 250-1500 mg/L H.sub.3PO.sub.4.

(31) At steady-state operation of the biohydrogenator, acetic and butyric acids were the predominant VFAs in the reactor, at concentrations of 2500 mg/L and 1600 mg/L, respectively. A hydrogen yield of 2.8 mol H.sub.2/mol glucose was achieved at a hydrogen production rate of 10 L H.sub.2/L.sub.reactor/d.

(32) The dark fermentation COD mass balance at steady-state operation including biomass yield can be written as follows:
8.56 gCOD (glucose).fwdarw.2.675 gCOD (acetic acid)+2.896 gCOD (butyric acid)+1.905 gCOD (hydrogen)+1.08 gCOD (biomass)(5)

(33) It is expected that after the system reaches steady-state fermentation, the following reactions will occur, if an external voltage ranging from 0.5 V to 0.9 V is applied, assuming an efficiency of 75%:
2.675 gCOD (acetic acid).fwdarw.2 gCOD (hydrogen)+0.461 gCOD (acetic acid)+0.214 gCOD (biomass)(6)
2.896 gCOD (butyric acid).fwdarw.2.172 gCOD (hydrogen)+0.494 gCOD (butyric acid)+0.23 gCOD (biomass)(7)

(34) Therefore, the expected overall process performance (dark fermentation+electro-assistance) can be predicted in the following COD mass balance equation:
8.56 gCOD (glucose).fwdarw.6.07 gCOD (hydrogen)+0.461 gCOD (acetic acid)+0.494 gCOD (butyric acid)+1.524 gCOD (biomass)(8)

(35) It is expected that application of an external voltage of 0.5 V to 0.9 V will increase hydrogen yield by a factor of about 3. The energy required for the external voltage is equivalent to 1 to 1.5 mole hydrogen/mole glucose. Thus, the net hydrogen yield is expected to be 7 to 7.5 mole hydrogen/mole glucose. Consequently, since 1 electron is required for every molecule in 7, every 14 grams of H.sub.2 produced requires 6.02210.sup.23 electrons (since 1 mol is 6.02210.sup.23 molecules and H.sub.2 has a molar mass of about 2 g/mol).

Example II

Systems Set Up and Operations

(36) A lab-scale system as shown in FIG. 1 was operated at 37 C. for 15 days, with an organic loading rate of 20 gCOD/L-d. The HRT was 8 hr and the SRT was estimated at 2.3 days. The system is an electro-assisted integrated biohydrogen reactor clarifier system, and included a CSTR for biological hydrogen production (5 L working volume) hydraulically connected to an uncovered (i.e. open to atmosphere) gravity settler (volume 8 L) for the decoupling of SRT from the HRT. In order to enrich hydrogen producing bacteria, prior to start-up, anaerobic digester sludge from the St. Marys wastewater treatment plant (St. Marys, Ontario, Canada) was heat treated in a baker at 70 C. for 30 minutes and was then used to seed the system. The system was monitored for COD, soluble COD, VFAs, ethanol, lactate, glucose, volatile suspended solids (VSS), total suspended solids and biogas composition including hydrogen, methane and nitrogen. The quantity of produced biogas was recorded using a wet tip gas meter (Rebel wet-tip gas meter company, Nashville, Tenn., USA).

(37) FIG. 4 shows the biohydrogen reactor used in the lab-scale system. The voltage was applied to the biohydrogen reactor through four pairs of electrodes. The anodes were made of graphite brushes (25 mm diameter150 mm length; fiber type; Gordon Brush Mfg Co., Inc., Commerce, Calif.) removed on one side to form half cylinder with specific surface area of 71.7 cm.sup.2/cm.sup.3-brush volume. The cathodes were made of carbon cloth 40 wt % Pt/C (Fuel Cell Earth Co., Inc) and stainless steel 304 mesh (mesh size #40, McMaster-Carr) with specific surface area of 2.54 cm.sup.2/cm.sup.2 attached to each other forming a cathode of one side carbon cloth and the other stainless steel mesh. The active surface area of four cathodes in total was 308 cm.sup.2 (3.5 m.sup.2/m.sup.3-reactor volume) for carbon cloth side and 914 cm.sup.2 (10 m.sup.2/m.sup.3-reactor volume) for the side covered with stainless steel mesh. The distance between the cathode and the anode of each electrode pair was 3 cm. The distance between the centers of an electrode pair and the next electron pair was 12 cm. For each pair of electrodes, a voltage of 1.0 V was applied using four separate power supplies (model 1665; BK Presision, Inc.). Each power supply had two leads; the negative lead was connected to the cathode and the positive lead was serially linked to an external resistance of 10 and to the anode. The current was calculated using Ohm's law (I=V/R), where V is the voltage drop across the 10 resistor measured using a multimeter (model 2700; Keithley Instruments, Inc.). After 3 days from start-up, when steady hydrogen production was established, power was applied in batch mode operation (i.e. 4 hours/day, once a day). During power application all the feed, effluent, and recycle pumps were switched off.

(38) Inocula and Media Compositions

(39) Anaerobically-digested sludge from the St. Marys wastewater treatment plant was used as the seed. The system was seeded with 5 liters of sludge and started up in a continuous dark fermentation mode for 4 days without power application. The feed contained 8 g/L of glucose and the following inorganics: 2000-4000 mg/L NaHCO.sub.3; 140 mg/L CaCl2; 160 mg/L MgCl.sub.2.6H.sub.2O; 600 mg/L NH.sub.4HCO.sub.3; 160 mg/L MgSO.sub.4.7H.sub.2O; 500-2000 mg/L urea; 124-300 mg/L Na.sub.2CO.sub.3; 156 mg/L KHCO.sub.3; 15-20 mg/L K.sub.2HPO.sub.4; 500 mg/L trace mineral solution; and 250-1500 mg/L H.sub.3PO.sub.4.

(40) Analytical Methods

(41) The biogas composition including H.sub.2, CH.sub.4, and N.sub.2 was determined by a gas chromatograph (Model 310, SRI Instruments, Torrance, Calif.) equipped with a thermal conductivity detector (TCD) and a molecular sieve column (Molesieve 5A, mesh 80/100, 6 ft in). Argon was used as carrier gas at a flow rate of 30 mL/min. The temperatures of the column and the TCD detector were 90 C. and 105 C., respectively. The concentrations of VFAs were analyzed using a gas chromatograph (Varian 8500, Varian Inc., Toronto, Canada) with a flame ionization detector equipped with a fused silica column (30 m0.32 mm). Helium was used as carrier gas at a flow rate of 5 mL/min. The temperatures of the column and detector were 110 C. and 250 C., respectively. Lactic acid concentrations were measured using a high-performance liquid chromatography system (1200 series, Agilent Technologies) equipped with Aminex HPX-87H ion exclusion column (300 mm7.8 mm I.D.; BIO-RAD), and a UV-detector at 210 nm. The column temperature was adjusted to 30 C. The same instrument with a refractive index detector (RID) was used to measure the concentrations of glucose. The temperature of the RID detector was set to 35 C. The amount of VSS and COD were measured according to standard methods.

(42) System Performance During Dark Fermentation Mode

(43) Steady-state was observed after 3 days from startup. The systems showed stable hydrogen production during the 30 days of operation. The coefficient of variation (calculated as standard deviation divided by the average) for hydrogen production rate and yield was less than about 15%. As summarized in Table 1, the hydrogen production rate averaged 1.75 L/h. The glucose conversion in the system was almost 100%. The hydrogen content in the biogas was around 60% with the balance CO.sub.2.

(44) TABLE-US-00001 TABLE 1 Summary of steady state data during dark fermentation mode (values are an average with standard deviation indicated). Dark Fermentation Mode Total Gas (L/h) 2.9 0.4 Hydrogen Gas (%) 60 5 Hydrogen Gas (L/h) 1.75 0.25 Hydrogen Gas (L/L/h) 0.35 0.05 Yield (mol H.sub.2/mol glucose) 2.8 0.2 Glucose Conversion (%) 99.9 1.5 % COD removed 40 10

(45) The biomass concentration in the reactor is an important operational parameter that affects both system stability and hydrogen yield. The average concentration of VSS in the biohydrogen reactor was 3900 mg/L. The COD mass balance, computed considering the measured influent and effluent CODs, and the equivalent CODs for both gas and biomass, are shown in Table 2. The closure of COD balance at 94% validates the reliability of the data. During the overall operational period the main liquid by-products were acetate, butyrate, and propionate at average concentrations of 2050 mg/L, 1150 mg/L, and 380 mg/L, respectively.

(46) TABLE-US-00002 TABLE 2 Summary of products and COD mass balance Measured parameters Dark Fermentation Mode VSS reactor (mg/L) 3900 410 VSS out (mg/L) 680 50 VSS out (mg COD/L) .sup.a 965 100 SCOD out (mg/L) 5100 750 Acetate (mg/L) 2050 250 Propionate (mg/L) 380 90 Isobutyrate (mg/L) 0 Butyrate (mg/L) 1150 210 Isovalerate (mg/L) 0 Valerate (mg/L) 0 Ethanol (mg/L) 0 Lactate (mg/L) 0 VFA (mg COD/L) 4860 Glucose Out (mg/L) 0 Hydrogen Gas (L/h) 1.75 0.25 Hydrogen Gas 1.1 (g COD/h) .sup.b COD balance (%) .sup.c 94 8 .sup.a Based on 1.42 g COD/g VSS .sup.b Based on 8 g COD/g H2 .sup.c COD balance (%) = ((VSSout (g COD/d) + H2 (g COD/d) + SCODout (g COD/d))/(TCODin (g COD/d))

(47) System Performance During Power Application Mode

(48) After 3 days of start-up of dark fermentation mode, and when hydrogen production was steady at 1.75 L/h, an external voltage of 1.0 V was applied to the four electrodes using four separate power supplies. The voltage was applied in cyclic mode for 4 hours per day. A total of 12 cycles of voltage application were applied over a period of 12 days. During power application cycles, acetate consumption and hydrogen content and volume were monitored.

(49) FIGS. 5 to 7 show the acetate consumption and volumetric hydrogen production for cycles 10, 11, and 12 of power application, respectively. The acetate concentrations showed a declining trend from about 2000 mg/L to 1000 mg/L (50% reduction) over a period of 4 hr. In each of the last 3 cycles, the acetate consumption was around 10%, 20%, 35%, and 50% at 1 hr, 2 hr, 3 hr, and 4 hr, respectively. Volumetric hydrogen production an increasing trend and reached a maximum of 2.9 L.

(50) As shown in Table 3, the average hydrogen content in the headspace was 65%. The maximum volumetric hydrogen production rate was 0.8 L/h. Acetate conversion averaged 57.6%. Based on the amount of hydrogen gas produced and acetate consumed an average hydrogen yield of 1.53 mole H.sub.2/mol acetate was achieved (38% of theoretical). The COD removal efficiency was close to 45%.

(51) TABLE-US-00003 TABLE 3 System performance during power application mode (values are an average with standard deviation for the last 3 cycles of power application indicated). Power application Mode Total Hydrogen Gas (L) 2.6 .3 Hydrogen Gas (%) 65 8 Hydrogen Gas (L/h) 0.65 .15 Hydrogen Gas (L/L/h) 0.132 .038 Yield (mol H.sub.2/mol Acetate) 1.53 0.3 Acetate Conversion (%) 57.6 6 % COD removed 43

CONCLUSIONS

(52) The following conclusions can be drawn from the experiment with application of both dark fermentation and power application: the overall maximum hydrogen yield that was achieved in process was 6.66 mol H.sub.2/mol glucose; the overall COD removal efficiency was around 77%; and H.sub.2 content of biogas ranged from 60% to 65% and hydrogen production rate from 0.132 L/L/h to 0.35 L/L/h.

Examples Only

(53) For purposes of illustration and not limitation, an integrated method and system for hydrogen and methane production from industrial organic waste and biomass is disclosed herein. As required, embodiments of the method and system are disclosed herein. However, the disclosed embodiments are merely exemplary, and it should be understood that the method and system may be embodied in many various and alternative forms.

(54) The figures are not to scale and some features may be exaggerated or minimized to show details of particular features while other features may have been eliminated to prevent obscuring aspects. Therefore, specific structural and functional details disclosed in the figures are not to be interpreted as limiting but merely as a basis for the claims and as a representative basis for teaching one skilled in the art to variously employ the present method and system.

(55) The scope of the claims should not be limited by particular embodiments set forth herein, but should be construed in a manner consistent with the specification as a whole.